The present invention is directed to the field of reading documents electronically and recreating the information read from the documents generally at a remote locality. More particularly, the present invention is directed to a device for removing noise from the binary signals that result from the scanning of documents such as bank checks. The present invention was designed as part of an automatic check processing system and has particular utility in automatic document processing systems such as facsimile and optical character recognition systems.
Images of documents contain many shades of gray called gray levels. Each gray level can be represented by a number called a gray value. In systems that process such signals as many as 64 gray levels are distinguished. In automatic document processing systems, gray levels are changed to numbers and a matrix of numbers is processed. In this matrix, each number of the matrix corresponds to the average gray value within a small square shaped area of the document. Each element is referred to as a "picture element" or a "pixel". In document processing, a matrix of gray values, where the number of gray levels is greater than 2, is called a "multi-gray level image" as compared to a "two-level" or "two-tone" image. For simplification, multi-gray level images are generally referred to as gray images, while the two-tone images are generally referred to as binary images. Binary images contain only the numbers 1 and 0 for black and white pixels, respectively.
The information appearing on, for example, most checks, is comprised of the legal and/or printed information along with the scenic background. This information can be represented by binary values where a 1 corresponds to a pixel covered by ink and a 0 corresponds to the pixel where there is little or no ink. In automatic document processing systems, it is desirable to use binary values rather than the gray image values because of the simplicity of handling 1's and 0's with computers. Such being the case, gray images are generally converted to binary images. During this process, called binarization, some pixels that do not belong to the 1 level are assigned a value of 1. This occurs because in addition to the legitimate information appearing on the checks, there is the background scene or pattern which can be as dark as the legal or desired information. The pixels in such dark areas are erroneously deemed black by the binarizer. These spurious black pixels are called noise. Additional causes of noise are, dirt on the paper, ink smudges, smears and the like. Noise has several detrimental effects on overall system performance in that it can often mislead computers and sometimes humans in their ability to recognize characters. It can also increase the amount of compressed image data by reducing the effectiveness of data compression algorithms. This in turn increases the space and cost associated with storing and transmitting the imaged data. And lastly, when the document is recreated on a visual screen, it strains the human eye during inspection due to the unclear images. Faced with the foregoing effects, it is highly desirable to process the binary images with a noise cleaning device after the binarization operation. Generally speaking, a noise cleaner should eliminate the noise as much as possible without impairing the legal and/or printed information. It should also be simple and be able to process the information quickly. There is a trade-off between the amount of noise that can be eliminated and the cost of the hardware for accomplishing the elimination. The present invention directs itself to providing a good noise cleaning performance while utilizing simple and fast hardware structures.
The following list of patents is indicative of the state of the art areas in which the invention resides:
U.S. Pat. No. 3,624,606 entitled, Data Connection System, by R. Lefevre; PA0 U.S. Pat. No. 3,700,797 entitled, Facsimile Noise Deletion and Coding System, by R. E. Wernikoff; PA0 U.S. Pat. No. 3,997,912 entitled, Method and Apparatus for Automatic Patterning Correction, by H. J. Zsagar; PA0 U.S. Pat. No. 4,038,668 entitled, Apparatus for Producing Smooth and Continuous Graphic Displays from Intermittently Sampled Data, by W. T. Quarton; and PA0 U.S. Pat. No. 4,060,713 entitled, Analysis of Imager, by M. J. E. Golay.